Hydraulic Hybrid Boom System Hydraulic Transformer

ABSTRACT

A hydraulic system includes a hydraulic actuator, an accumulator, an accumulator charge valve, and a hydraulic transformer fluidly connected between the accumulator charge valve and the accumulator. The hydraulic transformer includes a transformer motor mechanically coupled to a transformer pump. The accumulator charge valve is fluidly connected between the transformer motor and the hydraulic actuator. The transformer pump is sized to permit a maximum flow therethrough of no more than three-quarters of a flow permitted through the transformer motor.

TECHNICAL FIELD

The present disclosure relates generally to an electro-hydraulic system and, more particularly, to an electro-hydraulic system for recovering and reusing potential energy.

BACKGROUND

A machine (e.g., a wheel loader, an excavator, a front shovel, a bulldozer, a backhoe, a telehandler, etc.) may be used to move heavy loads, such as earth, construction material, and/or debris. The machine may utilize an implement to move the loads. The implement may be powered by a hydraulic system that may use pressurized fluid to actuate a hydraulic actuator to move the implement.

During operation of the machine, the implement may be raised to an elevated position. As the implement may be relatively heavy, the implement may gain potential energy when raised to the elevated position. Recovering that lost or wasted potential energy for reuse may improve machine efficiency.

U.S. Patent Publication No. 2004/0000141A1 to Nagura et al. discloses one system designed to recycle the energy associated with lowering a load. Return oil under pressure is supplied from an actuator and supplying circuit 13 through a pair of mechanically connected variable displacement hydraulic pumps/motors 1, 2 and a tank. Driven by hydraulic pump/motor 1 acting as a motor, hydraulic pump/motor 2 acts as a pump to supply oil to an accumulator 3 and/or a variable displacement hydraulic pump/motor 4, which, in turn may drive variable displacement hydraulic pump 5 to supply oil to a delivery line 16.

Components associated with energy recovery systems may not only be costly, but they may also require considerable space within such machines. Accumulators, for example, can be relatively large. As a result, the incorporation of energy recovery systems into smaller machine can present significant packaging challenges, sometimes preventing the inclusion of such systems entirely.

SUMMARY

The disclosure provides, in one aspect, a hydraulic system including a hydraulic actuator, an accumulator, an accumulator charge valve, and a hydraulic transformer fluidly connected between the accumulator charge valve and the accumulator. The hydraulic transformer includes a transformer motor mechanically coupled to a transformer pump. The accumulator charge valve is fluidly connected between the transformer motor and the hydraulic actuator. The transformer pump is sized to permit a maximum flow therethrough of no more than three-quarters of a flow permitted through the transformer motor.

The disclosure describes, in another aspect, a method of recovering and reusing energy with a hydraulic system. The method includes selectively actuating an accumulator charge valve to direct flow of hydraulic fluid from a hydraulic actuator to a transformer motor of a transformer unit, pumping no more than three-quarters of the hydraulic fluid flowing through the transformer motor by way of a transformer pump mechanically coupled to the transformer motor to an accumulator, selectively the accumulator charge valve to discontinue flow to the transformer motor, and selectively opening a discharge valve to direct flow from the accumulator to cause hydraulic fluid to be supplied to a hydraulic function.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a pictorial illustration of an exemplary disclosed machine;

FIG. 2 is a schematic illustration of an exemplary disclosed system that may be used in conjunction with the machine of FIG. 1, according to an embodiment

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 1 illustrates an exemplary machine 10 having multiple systems and components that cooperate to accomplish a task. The machine 10 may embody a fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or another industry known in the art. For example, the machine 10 may be an earth moving machine such as an excavator (shown in FIG. 1), a wheel loader, a front shovel, a bulldozer, a backhoe, a telehandler, a motor grader, a dump truck, or any other earth moving machine. The machine 10 may include an implement system 12 configured to move a work tool 14, a drive system 16 for propelling the machine 10, a power source 18 that provides power to the implement system 12 and the drive system 16, and an operator station 20 situated for manual control of the implement system 12, the drive system 16, and/or the power source 18.

The implement system 12 may include a linkage structure acted on by one or more hydraulic actuators, such as hydraulic cylinders, to move the work tool 14. The hydraulic actuators may include any device configured to receive pressurized hydraulic fluid, and convert a hydraulic pressure and/or flow from the pressurized hydraulic fluid into a mechanical force and/or motion. For example, the implement system 12 may also include a boom 22 and a stick 24 for pivotally connecting the work tool 14 to a body of the machine 10. In an embodiment, the boom 22 may be vertically pivotal about a horizontal axis relative to a work surface by one or more hydraulic actuators 30. As shown in FIGS. 1 and 2, a pair of adjacent, double-acting, hydraulic actuators 30 may pivotally connect the boom 22 to the body of the machine 10. The stick 24 may be pivotally connected at one end to the boom 22 and at the opposite end to the work tool 14. One or more hydraulic actuators may also be provided between the stick 24 and the work tool 14 in order to pivot the work tool 14, and/or between the boom 22 and the stick 24 in order to pivot the stick 24.

Numerous different work tools 14 may be attachable to a single machine 10 and may be operator controllable. The work tool 14 may include any device used to perform a particular task such as, for example, a bucket, a fork arrangement, a blade, a shovel, a ripper, a dump bed, a broom, a snow blower, a propelling device, a cutting device, a grasping device, or any other task-performing device known in the art. Although connected in the embodiment of FIG. 1 to pivot in the vertical direction relative to the body of the machine 10 and to swing in the horizontal direction, the work tool 14 may alternatively or additionally rotate, slide, open and close, or move in any other manner known in the art.

The power source 18 may embody an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of combustion engine known in the art. It is contemplated that the power source 18 may alternatively embody a non-combustion source of power such as a fuel cell, a power storage device, or another source known in the art. The power source 18 may produce a mechanical or electrical power output that may then be converted to hydraulic power for moving the hydraulic actuators 30 (and/or other hydraulic actuators) and/or one or more pumps as described below.

The operator station 20 may include devices that receive input from an operator indicative of desired machine maneuvering. Specifically, the operator station 20 may include one or more operator interface devices (e.g., a joystick, a steering wheel, a pedal, etc.) that are located proximate an operator seat. The operator interface devices may initiate movement of the machine 10 (e.g., travel and/or tool movement) by producing displacement signals that are indicative of desired machine maneuvering. As an operator moves the interface device, the operator may affect a corresponding machine movement in a desired direction, with a desired speed, and/or with a desired force.

As shown in FIG. 2, each hydraulic actuator 30 may include a housing 32 and a piston 34. The housing 32 may include a vessel having an inner surface forming an internal chamber. In an embodiment, the housing 32 may include a substantially cylindrically-shaped vessel having a cylindrical bore therein defining the inner surface. The piston 34 may be closely and slidably received against the inner surface of the housing 32 to allow relative movement between the piston 34 and the housing 32.

A rod 36 may be connected on one end to the piston 34, as shown in FIG. 2, and directly or indirectly to the boom 22 at another end of the rod 36, as shown in FIG. 1. The piston 34 may divide the internal chamber of the housing 32 into a rod-end chamber 38 corresponding to the portion of the internal chamber on the rod-end side of the housing 32, and a head-end chamber 40 corresponding to the portion of the internal chamber of the housing 32 opposite the rod-end side. The rod-end and head-end chambers 38, 40 may each be selectively supplied with pressurized fluid and drained of the pressurized fluid via respective apertures in the housing 32 to cause the piston 34 to displace within the housing 32, thereby changing an effective length of the hydraulic actuators 30, which moves the boom 22. A flow rate of fluid into and out of the rod-end and head-end chambers 38, 40 may relate to a translational velocity of the hydraulic actuators 30, while a pressure differential between the rod-end and head-end chambers 38, 40 may relate to a force imparted by the hydraulic actuators 30 on the associated linkage structure of implement system 12.

As illustrated in FIG. 2, the machine 10 may include a hydraulic circuit or system 50 having a plurality of fluid components that cooperate to selectively direct pressurized hydraulic fluid into and out of one or more hydraulic actuators to perform a task. For example, in the embodiment shown in FIG. 2, the hydraulic system 50 selectively directs pressurized hydraulic fluid into and out of the hydraulic actuators 30 to move the boom 22. The hydraulic system 50 may include a tank 52, a pump 54, a cylinder control valve assembly 60, and an energy recovery system 70. The hydraulic system 50 may also include other hydraulic actuators of the machine 10.

The tank 52 may include a source of low-pressure hydraulic fluid, such as, for example, a fluid reservoir. The fluid may include a dedicated hydraulic oil, an engine lubrication oil, a transmission lubrication oil, and/or other suitable working fluid. The hydraulic system 50 may selectively draw fluid from and return fluid to the tank 52 during operation of the implement system 12. Although only a single tank 52 is shown, it is also contemplated that the hydraulic system 50 may be in fluid communication with multiple, separate fluid tanks

The pump 54 may be configured to produce a flow of pressurized hydraulic fluid, and may include, for example, a piston pump, gear pump, vane pump, or gerotor pump. The pump 54 may have a variable displacement capacity, or, in the alternative, a fixed capacity for supplying the flow. The pump 54 may include a pump inlet 56 and a pump outlet 58. The pump inlet 56 may be connected to the tank 52 by a fluid line. In operation, the pump 54 may draw hydraulic fluid from the tank 52 at ambient or low pressure, and may convert mechanical energy or power to hydraulic energy or power by pressurizing the hydraulic fluid. The pressurized hydraulic fluid flow may exit through the pump outlet 58.

The pump 54 may include a stroke-adjusting mechanism, for example a swashplate, a position of which is hydro-mechanically or electro-hydraulically adjusted based on, among other things, a desired speed of the hydraulic actuators in the hydraulic system 50 (e.g., the hydraulic actuators 30) to thereby vary an output (e.g., a discharge rate) of the pump 54. The displacement of the pump 54 may be adjusted from a zero displacement position at which substantially no fluid is discharged from the pump 54, to a maximum displacement position at which fluid is discharged from the pump 54 at a maximum rate. The pump 54 may be drivably connected to the power source 18 by, for example, a countershaft, a belt, or in another suitable manner. Alternatively, the pump 54 may be indirectly connected to the power source 18 via a coupling, a torque converter, a gear box, an electrical circuit, or in any other manner known in the art. The pump 54 may be dedicated to supplying pressurized hydraulic fluid to the hydraulic actuators 30 and/or other hydraulic actuators of the machine 10.

The cylinder control valve assembly 60 may include an independent metering valve unit, including two pump-to-cylinder (“P-C”) independent metering control valves 62 and 64 and two cylinder-to-tank (“C-T”) independent metering control valves 66 and 68. The P-C and C-T independent metering control valves 62, 64, 66, and 68 may each be independently actuated into open and closed conditions, and positions between open and closed. Through selective actuation of the P-C and C-T control valves 62, 64, 66, and 68, pressurized hydraulic fluid may be directed into and out of the rod-end and head-end chambers 38, 40 of each hydraulic actuator 30. By controlling the direction and rate of fluid flow to and from the rod-end and head-end chambers 38, 40, the P-C and C-T control valves 62, 64, 66, and 68 may control the motion of the implement system 12. Additionally or alternatively, the cylinder control valve assembly 60 may include one or more single spool valves (not shown), proportional control valves, or any other suitable devices configured to control the rate of pressurized hydraulic fluid flow entering into and exiting out of the hydraulic actuators 30.

The P-C control valves 62 and 64 may be configured to direct pressurized hydraulic fluid exiting from the pump outlet 58 into the hydraulic actuators 30. In an embodiment, the P-C control valve 62 may selectively direct hydraulic flow into the head-end chambers 40 of the hydraulic actuators 30 (e.g., via one or more fluid lines that fluidly connect the P-C control valve 62 to the head-end chambers 40 in parallel), and the P-C control valve 64 may selectively direct hydraulic flow into the rod-end chambers 38 (e.g., via one or more fluid lines that fluidly connects the P-C control valve 64 to the rod-end chambers 38 in parallel). Also, the P-C control valves 62 and 64 may be configured to fluidly connect the head-end chambers 40 and the rod-end chambers 38.

The C-T control valves 66 and 68 may be configured to direct hydraulic fluid exiting from the hydraulic actuators 30 to the tank 52. In an embodiment, the C-T control valve 66 may receive hydraulic fluid leaving the head-end chambers 40 and direct the hydraulic fluid towards the tank 52 (e.g., via one or more fluid lines that fluidly connect the head-end chambers 40 in parallel to the C-T control valve 66). The C-T control valve 68 may receive hydraulic fluid leaving the rod-end chambers 38 and direct the hydraulic fluid towards the tank 52 (e.g., via one or more fluid lines that fluidly connect the rod-end chambers 38 in parallel to the C-T control valve 68). The C-T control valves 66 and 68, like the P-C control valves 62 and 64, may include various types of independently adjustable valve devices.

In an embodiment, the energy recovery system 70 may include a high-pressure (“HP”) accumulator 72, an accumulator charge valve 74, check valve 76, a transformer unit 77, a motor discharge valve 82, and a torque assistance motor 84. It will be appreciated that, in an alternate embodiment, a variable-displacement over-center pump/motor (not illustrated) and its associated fluid lines may be substituted for the torque assistance motor 84 and its associated fluid lines shown in FIG. 2. The energy recovered by the energy recovery system 70 may be used to provide power for subsequent movements and operations of the hydraulic actuators 30 and/or other hydraulic actuators of the machine 10.

For example, the energy recovery system 70 may recover energy associated with the pressurized hydraulic fluid discharged from the hydraulic actuators 30 under an overrunning load condition. An overrunning load condition may exist when retraction is desired after the hydraulic actuators 30 have been extended to lift a load. In the overrunning load condition, the hydraulic actuators 30 may be retracted by the force of gravity on the implement system 12 and/or the force of gravity on the load carried by the implement system 12 (e.g., by opening the P-C control valve 64 and closing the P-C control valve 62 and the C-T control valve 68). This retraction may cause movement of the pistons 34 in the direction of the respective head-end chambers 40, thus resulting in pressurized hydraulic fluid being forced out of the head-end chambers 40. The overrunning load condition may be distinguished from a resistive load condition where the hydraulic actuators 30 must work against the weight of the implement system 12 and/or the force of gravity on the load to perform a movement or operation. The resistive load condition may exist when extending the hydraulic actuators 30, e.g., lifting the pistons 34 against the force of gravity.

The hydraulic transformer unit 77 includes a transformer motor 78 and a transformer pump 79, which are mechanically coupled to one another, and fluidly coupled to a tank 52. The transformer motor 78 may be a fixed-displacement motor, such as is illustrated or a variable displacement motor. Similarly, the transformer pump 79 may be a fixed or variable displacement pump. The transformer motor 78 may be connected to a shaft of the transformer pump 79. Alternatively, the transformer pump 79 may be connected to the transformer motor 78 via another mechanical arrangement, such as one or more mechanical connectors, e.g., gears, shafts, couplers, etc.

According to an aspect of the disclosure, the displacement of the transformer pump 79 has a maximum displacement of less than the displacement of the transformer motor 78. More particularly, the maximum displacement of the transformer pump 79 is a fraction of the displacement of the transformer motor 78. Hydraulic fluid flowing through the transformer motor 78 that is in excess of the hydraulic fluid flowing through the transformer pump 79 may be direct to a tank 52. In an embodiment, flow from the transformer pump 79 is a maximum of three-quarters of the flow through the transformer motor 78. In yet another, more particular embodiment, flow from the transformer pump 79 is a maximum on the order of one-half of that of the flow from the transformer motor 78. As a result, the hydraulic fluid pressure at the outlet of the transformer pump 79 is twice that of the fluid pressure at the inlet to the transformer motor 78. This higher pressure at the outlet of the transformer pump 79 facilitates the flow of hydraulic fluid to and building of pressure in the accumulator 72. The significance of the comparative flows will be further discussed below.

The accumulator charge valve 74 may fluidly connect the head-end chambers 40 to the transformer motor 78. In the overrunning load condition, the accumulator charge valve 74 may be actuated to an open position while the C-T control valve 66 may be actuated to a closed position, thus allowing pressurized hydraulic fluid exiting the head-end chambers 40 to drive the transformer motor 78 and flow to the tank 52. The accumulator charge valve 74 may work in conjunction with the check valve 76 such that when the accumulator charge valve 74 is in the open position, the check valve 76 may allow pressurized hydraulic fluid to flow from the head-end chambers 40 toward the transformer motor 78, but not in the reverse direction. In non-overrunning load conditions (such as the resistive load condition), the accumulator charge valve 74 may be in a closed position to prevent entry of pressurized hydraulic fluid exiting the head-end chambers 40 to the transformer motor 78 (or vice versa).

With the accumulator charge valve 74 open, fluid exiting the head-end chambers 40 drives the transformer motor 78, as well as the mechanically coupled transformer pump 79. As a result, the transformer pump 79 pumps hydraulic fluid from the tank 52 to enter (or charge) the accumulator 72.

The accumulator 72 may be discharged to any hydraulic function of the hydraulic system 50. In the illustrated embodiment, for example, the motor discharge valve 82 may be located in a fluid line that fluidly connects the accumulator 72 to the torque assistance motor 84 to reuse (or discharge) the pressurized hydraulic fluid stored in the accumulator 72.

In an overrunning load condition, the motor discharge valve 82 may be in a closed position and the accumulator charge valve 47 in an open position. As a result, pressurized hydraulic fluid exiting from the head-end chambers 40 flows to and operates the transformer motor 78, and the mechanically coupled transformer pump 79 pumps fluid toward the accumulator 72. As the hydraulic fluid flowing from the transformer pump 79 enters the accumulator 72, pressure within the accumulator 72 increases, thus making it more difficult to pump hydraulic fluid to the accumulator 72. In order to minimize the opportunity for an increase in torque at the transformer pump 79, and, accordingly, an attendant reduction in the performance of the transformer motor 78, as the pressure within the accumulator 72 increases, flow may be decreased from the transformer pump 79, as by reducing the angle of a swashplate (not shown) in a variable displacement transformer pump 79 to reduce or eliminate flow. In this way, the flow through the transformer motor 78 is maintained, with the remainder of the flow from the transformer motor 78 being directed to the tank 52, the speed and displacement of the transformer motor 78 being maintained. Alternately, in some embodiments, the transformer pump 79 may be decoupled from the transformer motor 78 to eliminate flow through the transformer pump 79 and direct all of the flow through the transformer motor 78 to the tank 52. Alternately or additionally, the motor discharge valve 82 may be opened to allow the pressurized fluid to flow to the torque assistance motor 84 and the tank 52 in an overrunning load condition. Further, in situations where pressure within the accumulator 72 exceeds the pressure at relief valve 106, flow may be directed to the tank 52 through the relief valve 106.

When extension of the hydraulic actuators 30 is desired, e.g., in the resistive load condition or other non-overrunning load condition, the motor discharge valve 82 may be shifted to an open position so that the pressurized hydraulic fluid stored in the accumulator 72 may be reused. With the accumulator charge valve 74 in a closed position and the transformer pump 79 not operative, a flow path is created between the accumulator 72 and the torque assistance motor 84 such that pressurized hydraulic fluid in the accumulator 72 may be supplied to the torque assistance motor 84 to produce a mechanical energy output (e.g., to assist in driving the pump 54). For example, the pressurized hydraulic fluid may be supplied by the accumulator 72 to the hydraulic actuators 30 to perform a desired movement and/or to the torque assistance motor 84 to generate mechanical energy output.

The torque assistance motor 84 may be a variable-displacement motor coupled to the power source 18 and/or the pump 54. The torque assistance motor 84 may be configured to receive pressurized fluid from the accumulator 72 and discharge the fluid into the tank 52. The torque assistance motor 84 may use the energy contained within the pressurized fluid to generate a mechanical energy output that is passed to the pump 54 and/or other components. For example, as shown in FIG. 2, the motor 84 may be connected to a pump shaft of the pump 54, and the pump shaft may also be driven by the power source 18. Alternatively, the pump 54 may be connected to the torque assistance motor 84 and/or the power source 18 via another mechanical arrangement, such as one or more mechanical connectors, e.g., gears, shafts, couplers, etc.

The energy recovery system 70 may also include a check valve 92, a back pressure valve 94, and one or more additional accumulators (not shown). The back pressure valve 94 may allow passage of pressurized hydraulic fluid back into the tank 52. For example, pressurized hydraulic fluid leaving the rod-end chambers 38 may be directed through C-T control valve 68. Once the pressure from the C-T control valve 68 exceeds a predetermined pressure, the back pressure valve 94 may be forced into an open position, thus allowing the pressurized hydraulic fluid to flow to the tank 52. Once fluid pressure from the C-T control valve 68 falls back below the predetermined pressure, then the back pressure valve 94 may return to its closed position. It is contemplated that the predetermined pressure level may be adjusted by adjusting the biasing pressure exerted by the back pressure valve 94.

During operation of the machine 10, the operator of the machine 10 may utilize the interface device (not shown) to provide a signal that identifies a desired movement of the hydraulic actuators 30 to a controller 100. Based upon one or more signals, including the signal from the interface device (not shown) and, for example, signals from various pressure, temperature, and/or position sensors 102 located throughout the hydraulic system 50, the controller 100 may command movement of the different valves 62, 64, 66, 68, 74, and 82 and/or displacement changes of the pump 54 and the torque assistance motor 84 to move the hydraulic actuators 30 to a desired position in a desired manner (i.e., at a desired speed and/or with a desired force). For example, the sensors 102 may include an accumulator pressure sensor 102A configured to determine a pressure associated with the pressurized hydraulic fluid stored in and/or supplied to the accumulator 72, one or more cylinder pressure sensors 102B configured to determine a pressure associated with the pressurized hydraulic fluid stored in and/or supplied to the head-end chambers 40, and/or a pump pressure sensor 102C configured to determine a pressure associated with the pressurized hydraulic fluid supplied from the pump 54. As shown in FIG. 2, other sensors may be provided, such as sensors 102 configured to determine a temperature of the pressurized hydraulic fluid stored in the accumulator 72, a pressure of the hydraulic fluid directed from the motor discharge valve 82 to the torque assistance motor 84, a displacement of the torque assistance motor 84, spool displacement sensors for the respective P-C control valves 62 and 64, a pressure of the hydraulic fluid supplied from the pump 54 and directed to the P-C control valves 62 and 64, and pressures of the hydraulic fluid stored in, supplied to, or discharged from the respective rod-end and head-end chambers 38 and 40. While not shown in detail, each of the sensors 102 valves 62, 64, 66, 68, 74, and 82, and the pumps 54, 79 may include connections to the controller 100 for transmitting and receiving signals regarding operation of the same.

The controller 100 may embody a single microprocessor or multiple microprocessors that include components for controlling operations of the hydraulic system 50 based on input from an operator of the machine 10 and based on sensed or other known operational parameters. Numerous commercially available microprocessors can be configured to perform the functions of the controller 100. It should be appreciated that the controller 100 could readily be embodied in a general machine microprocessor capable of controlling numerous machine functions. The controller 100 may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with the controller 100 such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry.

One or more additional check valves 104 may be provided to assist in regulating the flow of hydraulic fluid, e.g., discharged from the pump 54 and/or the hydraulic actuators 30. Also, one or more relief valves 106 may be provided to allow fluid relief from the hydraulic system 50 into the tank 52 when a pressure of the hydraulic fluid exceeds a set threshold of the relief valve 106.

INDUSTRIAL APPLICABILITY

The disclosed hydraulic system 50 may have particular applicability with machines to allow recovery and/or reuse of potential energy associated with movement of the implement system 12 operatively connected to one or more hydraulic actuators (e.g., the hydraulic actuators 30) or other hydraulic actuators.

Inasmuch as the displacement of the transformer pump 79 is a fraction of the displacement of the transformer motor 78, yielding a relatively higher pressure flow from the transformer pump 79 than the flow into the transformer motor 78. In an embodiment, flow from the transformer pump 79 may be on the order of one-half of that of the flow from the transformer motor 78, although the flow from the transformer pump 79 may be within a range of less than 75% of flow from the transformer motor 78. In an embodiment where the flow from the transformer pump 79 is one half the volume of flow into the transformer motor 78, the pressure of hydraulic fluid at the outlet of the transformer pump 79 will be roughly twice the pressure of hydraulic fluid entering the transformer motor 78.

As a result, the use of the hydraulic transformer unit 77 may facilitate the use of a relatively smaller accumulator 72 than is utilized in many energy recovery systems. For example, in an embodiment, an accumulator 72 of 64 liters may be utilized. In alternate embodiments, accumulators 72 ranging in volume from 20 to 45 liters may be utilized.

Further, those of skill will appreciate that some embodiments of the disclosed energy recovery system 70 may be packaged in machines 10 that could not accommodate a large accumulator associated with prior art energy recovery systems, allowing for desirable energy recovery, even in relatively small machines.

In some embodiments, the use of a hydraulic transformer unit 77 including a transformer pump 79 having a flow proportionally less than the flow into the transformer motor 78 may facilitate building the use of adequate pressure within a smaller accumulator than is generally utilized in an energy recovery system 70.

Operation of the hydraulic system 50 will now be described in greater detail.

During operation of the machine 10, an operator located within the operator station 20 may command a particular motion of work tool 14 in a desired direction and at a desired velocity by way of an interface device. One or more corresponding signals generated by the interface device may be provided to the controller 100 indicative of the desired motion, along with machine performance information, for example data from the sensors 102 such pressure data, position data, temperature data, speed data, pump and/or motor displacement data, and other data known in the art.

The controller 100 may generate control signals directed to one or more of the pump 54, the torque assistance motor 84, the valve(s) 62, 64, 66, 68, 74, 82, and/or other components of the hydraulic system 50. For example, based on the signals from the interface device, the controller 100 may determine whether to extend or retract the hydraulic actuators 30, and the speed and direction of movement of the hydraulic actuators 30. The controller 100 may also determine whether to open the accumulator charge valve 74 to charge the accumulator 72. The controller 100 may also determine whether to discharge the accumulator 72 to supply the pressurized hydraulic fluid to the torque assistance motor 84 (e.g., by opening the motor discharge valve 82) to assist in driving the pump 54 or other components.

Refraction of the hydraulic actuators 30 to lower the boom 22 from a raised position may be driven by the force of gravity acting on the raised boom 22 and/or the force of gravity on the load carried by the work tool 14. Those forces may act on the pistons 34 to push pressurized hydraulic fluid out of the head-end chambers 40. That pressurized hydraulic fluid may then be directed to the transformer motor 78 via the accumulator charge valve 74. The flow of hydraulic fluid through the transformer motor 78 drives the transformer pump 79 to provide a higher pressure hydraulic fluid flow into the accumulator 72, where it may be stored and/or directed to an alternate operation. In the illustrated embodiment, hydraulic fluid under pressure may be directed to drive the torque assistance motor 84, to assist pump 54 in delivery of fluid to the cylinder control valve assembly 60, and, more specifically, the P-C control valves 62 and 64 to assist in maintaining a desired speed for the retraction of the hydraulic actuators 30.

Extension of the hydraulic actuators 30 to raise the boom 22 may include supplying pressurized hydraulic fluid, provided by the pump 54, into the head-end chambers 40 while allowing pressurized hydraulic fluid in the rod-end chambers 38 to return to the tank 52.

The stored pressurized hydraulic fluid in the accumulator 72 may be used to provide power to assist in subsequent movements of the boom 22, by providing hydraulic fluid under pressure to the torque assistance motor 84, which provides torque to the pump 54 to extend the hydraulic actuators 30. For example, the controller 100 may open the motor discharge valve 82 to supply the pressurized hydraulic fluid from the accumulator 72 to the torque assistance motor 84 to assist in driving the pump 54.

Thus, the energy recovery system 70 may provide for the recovery and/or reuse of energy by capturing the energy which was previously throttled to tank and lost as heat, and by storing the energy in the accumulator 72. Then, when an operator desires to once again raise the boom 22 by extending the hydraulic actuators 30, the stored energy, in the form of pressurized hydraulic fluid, may be provided to torque assistance motor 84. This reuse of energy may improve machine efficiency and reduce fuel costs (e.g., by helping to reduce a load on the power source 18) and overall operating costs, while still satisfying operator demands.

It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.

The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context.

Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. 

I claim:
 1. A hydraulic system comprising: a hydraulic actuator; an accumulator; an accumulator charge valve; and a hydraulic transformer unit fluidly connected between the accumulator charge valve and the accumulator, the hydraulic transformer unit including a transformer motor mechanically coupled to a transformer pump, the accumulator charge valve being fluidly connected between the transformer motor and the hydraulic actuator, the transformer pump being sized to permit a maximum flow therethrough of no more than three-quarters of a flow permitted through the transformer motor.
 2. The hydraulic system of claim 1 wherein the transformer pump is sized to permit a maximum flow therethrough of no more than one-half of a flow permitted through the transformer motor, excess flow from the transformer motor that does not flow to the transformer pump being directed to a tank.
 3. The hydraulic system of claim 1 further including a discharge valve fluidly connected to the accumulator to control flow out of the accumulator.
 4. The hydraulic system of claim 3 wherein the discharge valve is selectively operable to supply stored fluid from the accumulator to cause fluid to be supplied to a hydraulic function.
 5. The hydraulic system of claim 1 further including a pump configured to supply fluid to the hydraulic actuator, and a torque assistance motor drivingly connected to the pump and fluidly connected to the accumulator, the torque assistance motor being configured to receive stored fluid from the accumulator to drive the pump.
 6. The hydraulic system of claim 5 further including a discharge valve fluidly connected between the accumulator and the torque assistance motor, the discharge valve being configured to supply stored fluid from the accumulator to the torque assistance motor.
 7. The hydraulic system of claim 2 wherein the accumulator is sized to contain a maximum of sixty-four liters of hydraulic fluid.
 8. The hydraulic system of claim 1 further including a controller connected to the charge valve, the controller being configured to receive a command to retract the hydraulic actuator, and in response to the command, open the charge valve.
 9. The hydraulic system of claim 3, further including a controller connected to the discharge valve, the controller being configured to receive a command to provide fluid to the hydraulic actuator, and in response to the command, open the discharge valve to discharge stored fluid from the accumulator.
 10. The hydraulic system of claim 6, further including a discharge valve fluidly connected between the accumulator and the torque assistance motor, the discharge valve being configured to supply the stored fluid from the accumulator to the torque assistance motor.
 11. The hydraulic system of claim 5, wherein: the hydraulic actuator is a hydraulic cylinder configured to move a boom that is movably connected to a body of a machine, the hydraulic cylinder being one of a plurality of hydraulic cylinders, the pump is selectively configured to supply fluid to a plurality of first chambers of the plurality of hydraulic actuators in parallel and supply fluid to a plurality of second chambers of the plurality of hydraulic actuators in parallel; in an overrunning load condition, the accumulator is configured to store fluid received from the plurality of first chambers; and in a non-overrunning load condition, the torque assistance motor is configured to receive the stored fluid from the accumulator to drive the pump to supply fluid to the plurality of first chambers.
 12. A method of recovering and reusing energy with a hydraulic system, the method comprising: selectively actuating an accumulator charge valve to direct flow of hydraulic fluid from a hydraulic actuator to a transformer motor of a transformer unit; pumping no more than three-quarters of the hydraulic fluid flowing through the transformer motor by way of a transformer pump mechanically coupled to the transformer motor to an accumulator; selectively the accumulator charge valve to discontinue flow to the transformer motor; and selectively opening a discharge valve to direct flow from the accumulator to cause hydraulic fluid to be supplied to a hydraulic function.
 13. The method of claim 12 wherein pumping no more than three-quarters of the hydraulic fluid flowing through the transformer motor includes the transformer pump pumping no more than one-half of the flow through the transformer motor to the accumulator.
 14. The method of claim 13 wherein the accumulator is sized to receive no more than sixty-four liters of hydraulic fluid.
 15. The method of claim 13 wherein selectively opening the discharge valve includes directing flow to a torque assistance motor, and the torque assistance motor at least partially powering a pump to cause hydraulic fluid to be supplied to the hydraulic actuator.
 16. The method of claim 12 further including sensing a pressure in the accumulator, and at least one of the following when pressure within the accumulator nears its maximum reducing flow through the transformer pump, opening the discharge to permit flow to bypass the accumulator, or relieving pressure by venting hydraulic fluid to a tank through a relief valve.
 17. The method of claim 13 wherein selectively actuating the accumulator charge valve to direct flow from the hydraulic actuator includes selectively actuating the accumulator charge valve to direct flow from a plurality of head-end chambers of a plurality of hydraulic cylinders to the transformer motor, and the selectively opening the discharge valve includes selectively opening the discharge valve to direct flow to a torque assistance motor, and operating the torque assistance motor to assist in operation of a mechanically coupled hydraulic pump to supply fluid to a plurality of rod-end chambers of the plurality of hydraulic cylinders.
 18. A machine comprising: at least one hydraulic actuator; a pump configured to supply hydraulic fluid to the hydraulic actuator; a power source configured to supply power to drive the pump, the power source including a torque assistance motor mechanically coupled to the pump; an accumulator; an accumulator charge valve; a hydraulic transformer unit fluidly connected between the accumulator charge valve and the accumulator, the hydraulic transformer unit including a transformer motor and a transformer pump, the accumulator charge valve being fluidly connected between the transformer motor and the hydraulic actuator, the transformer pump being mechanically coupled the transformer motor, the transformer pump being sized to permit a maximum flow therethrough of no more than three-quarters of a flow permitted through the transformer motor; and a discharge valve fluidly connected between the accumulator and the torque assistance motor.
 19. The machine of claim 18, wherein the accumulator is sized to hold no more than 64 liters of hydraulic fluid.
 20. The machine of claim 18, wherein the transformer pump is sized to permit a maximum flow therethrough of no more than one-half of a flow permitted through the transformer motor, excess flow from the transformer motor that does not flow to the transformer pump being directed to a tank. 